udp: Add udp_sock_create for UDP tunnels to open listener socket

Added udp_tunnel.c which can contain some common functions for UDP
tunnels. The first function in this is udp_sock_create which is used
to open the listener port for a UDP tunnel.

Signed-off-by: Tom Herbert <therbert@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/net/udp_tunnel.h

@@ -0,0 +1,32 @@
+#ifndef __NET_UDP_TUNNEL_H
+#define __NET_UDP_TUNNEL_H
+
+struct udp_port_cfg {
+	u8			family;
+
+	/* Used only for kernel-created sockets */
+	union {
+		struct in_addr		local_ip;
+#if IS_ENABLED(CONFIG_IPV6)
+		struct in6_addr		local_ip6;
+#endif
+	};
+
+	union {
+		struct in_addr		peer_ip;
+#if IS_ENABLED(CONFIG_IPV6)
+		struct in6_addr		peer_ip6;
+#endif
+	};
+
+	__be16			local_udp_port;
+	__be16			peer_udp_port;
+	unsigned int		use_udp_checksums:1,
+				use_udp6_tx_checksums:1,
+				use_udp6_rx_checksums:1;
+};
+
+int udp_sock_create(struct net *net, struct udp_port_cfg *cfg,
+		    struct socket **sockp);
+
+#endif